I've found a lot of treasure on Cyborg 009, Sonic X, and Full Metal Panic. My advice is: if you find a treasure on a certain character, go to the series where that character's from and look at every other character in that series to see if there's treasure.

That's similar to one of my early strategies: Take a series with a lot of characters, say 70+ and check each one for a chest, open it, and scroll back to the title's character list and check the next one. It worked quite efficiently with franchises.